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Logging Tasks:
Q1) What wetland type do you see at the published coordinates?
Q2) Take a handful of sand at the published coordinates and examine it.
- Describe the colour and grain of the soil.
- From the various beach sand compositions mentioned hereunder state what you think the sand comprises here?
Q3) There is soil erosion at this waypoint S26 53.678 E32 51.774.
- What colour is the soil in this donga?
- What do you think causes it to be this colour?
Q4) What man-made object is found at this Waypoint? S26 53.728 E32 51.952
GENERAL LOCATION
The greater part of the Kosi System is situated between S26° 52’ to S27° 10’ and between E32° 42’ to E32° 54’ and it stretches from an east north-easterly to a south south-westerly direction. The system lies on the coastal plain west of the Lebombo Mountains in the north-eastern extremity of the Ingwavuma (also known as Tongaland or Maputaland) district. A small part of the catchment is situated in Mozambique.
The Kosi system is approximately 470km north east of Durban. The nearest town is Ingwavuma, situated 105 km from the estuary, although the village of KwaNgwanase is 13 km from the KwaZulu Department of Nature Conservation cam on the northwestern shores of Lake Nhlange.
OVERVIEW OF SITE
The Kosi Bay system is composed of four interconnected, roughly circular lakes Makhawulani, Mpungwini, Nhlange/Kosi Lake and Amanzamnyama, a broad channel leading to an estuary, which opens to the Indian Ocean and three extensive areas of swamp. The lakes are separated from the ocean by a strip of forested sand dunes 600 – 2000m in width.
The Kosi drainage area comprises approximately 500km2. There are 2 main rivers that form the system, mainly the Sihadhla River (+/- 30 km), which rises in the Mtombeni pans. This river receives water from 12 principal tributary systems. It enters the Kosi system at Lake aManzimnyama. The other main river is the Nswamanzi River (+/- 15km), which collects water from 9 principal tributaries and enters lake Nhlange on its western shore.
The lakes form part of the iSimangaliso Wetland Park, a UNESCO Worlk Heritage Site. Kosi Bay estuary is only 2 kilometres from the Mozambique border. It is possible to walk from the estuary to Ponta do Ouro in only an hour or so. It is one of the quietest beaches in South Africa. The Kosi River Mouth is known as “the aquarium” because of the clarity of the water and the abundance of fish species. This is Ramsar site No 527.
HISTORY
Kosi bay is an ancient home of the Tsonga people and their primitive fish traps (kraals). The history of Vatsonga people on this land dates back some 800 years ago, Kosi bay and Maputo bay was one land and they belonged to the Tsonga people. When Britain colonised South Africa, Kosi bay was annexed to Natal, while Maputo was annexed to Mozambique. The Vatsonga people lost large tracks of land on St Lucia bay in 1875 when Britain took the land and restricted the Tsonga people to Kosi bay only. Before 1875, the Tsonga people controlled the whole of St Lucia Bay, later to be known as Greater St Lucia Wetland Park. Today, Kosi bay continues to be the proud home of the Tsonga people, and chief Israel Tembe, the descendent of ancient Tembe kingdom, exercise political control over the bay, the Tembe Elephant Park testify to this ancient Tsonga history.
TOPOGRAPHY
The deepest area (northern trench) of Lake Nhlange is 31m. There are varied opinions about the size of the Kosi system, with the size of the Lake Nhlange being estimated between 30 and 37km2 in size. The Kosi system is a fine example of segmentation, a process whereby the system is transformed into circular water bodies, which are separated by low beach barriers.
GEOLOGY
The Kosi system lies within the pale sandy soils of the Mozambique Coastal Plain, which overlie cretaceous beds. The coastal dunes are composed of both Holocene and Pleistocene sand deposits.
Holocene is a geological epoch which began at the end of the Pleistocene (at 11,700 calendar years BP and continues to the present.
Pleistocene is a geological epoch which lasted from about 2 588 000 to 11 700 years ago, spanning the world’s recent period of repeated glaciations.
No rocks occur to the west of the coastal dunes, but on the coast, rock ledges, shelves and outcrops occur, one of which forms a small reef within the estuary upon which a very diverse fauna may be found.
The geology of the Maputaland area consists mostly of volcanic rocks of the Karoo event (basalts, rhyolites, tuffs, vitreous material and dolerites), which build up the Lebombo Mountains in the west and the sedimentary belt of Mozambique Coastal Plain.
The geology of the coastal plain can be summarised as a succession of Cretaceous to Quaternary sedimentary deposits.
The Cretaceous (meaning chalk), is a geologic period from 145 to 66 million years ago. The high eustatic sea level and warm climate of the Cretaceous meant a large area of the continents was covered by warm shallow seas. The Cretaceous was named for the extensive chalk deposits in many parts of the world. The Cretaceous system consists for a major part of marine limestone, a rock type that is formed under warm, shallow marine circumstances. Due to the high sea level there was extensive accommodation space for sedimentation so that thick deposits could form. Because of the relatively young age and great thickness of the system, Cretaceous rocks crop out in many areas worldwide.
The Quaternary Period spans from 2.588 ± 0.005 million years ago to the present. This relatively short geological period is characterized by a series of glaciations. The Quaternary includes two geologic epochs: the Pleistocene and Holocene. Pleistocene non-marine sediments are found primarily in fluvial deposits, lakebeds, slope and loess deposits as well as in the large amounts of material moved about by glaciers. Less common are cave deposits, travertines and volcanic deposits (lavas, ashes). Pleistocene marine deposits are found primarily in shallow marine basins mostly (but with important exceptions) in areas within a few tens of kilometers of the modern shoreline.
The dominant geology in Maputaland consists mostly of undulating sand dunes, which enclose coastal lakes and swamps with peat. Sand dunes cordons were probably formed along the shores of each still stand pause in overall phases of rising and especially of receding sea levels (Tinley 1985 see ref). During the last Glacial maximum, about 18 000 years BP, the sea level fell to about 130m below present sea level (Ramsay 1977 see ref). During this time the greater part of the continental shelf was exposed, there was for example a 130 km broad plain off Beira, central Mozambique and the Agulha Bank formed a 180 km broad, grass covered plain, transversed by the meandering floodplain drainage of the South Cape Rivers (Dingle and Rogers 1972 see ref). The largest dune fields were formed during this time when high wind velocity regimes blasted across massive deposits of exposed continental shelf sediments. The enclosed water bodies are remnants of a barrier lakes segmented by advancing parabolic dunes (U-shaped mounds of sand with convex noses trailed by elongated arms). Inland dunes are ancient oxidized and more or less lithified dunes, and display a red and/or yellowish colours in most cases. The coastal dunes are young, which occur as a narrow coastal cordon facing directly the beaches. These dunes are made up of old and modern dune sands.
Orme (see ref) is of the opinion that the surface water area of the Kosi River system has decreased by 68% since the Holocene transgression, due to sedimentation, segmentation and reed swamp encroachment.
Hemens et al (see ref) said that Lake Amanzimnyama has decreased in depth since in has acted primarily as a sedimentation basin.
The shallow entrance of the Kosi system is due to siltation, mainly because of substantial sand movement along the coast.
SOIL TYPE AND CHEMISTRY
The bottom materials in the Kosi System are principally clean, white sands, particularly in the northern most reaches where tidal influences are most marked. Sandy substrates are also characteristic even on steeply-shelving profiles and in the lake margins. The only silt is found in deeper waters, or as a thin layer overlying sand in certain shallow areas. The sandy substrates of Kosi are characterised by a lack of fine particles and are low in nutrient content. They contrast in these respects to the bottom materials of the deeper parts of the system where unconsolidated organic debris has collected. In these instances the bottom materials are characterised by low dry weights and high volatile and nutrient values. They can be of considerable thickness and are black and hydrogen and sulphide bearing. These materials originate in the marches and swamps alongside the system and then naturally gravitate towards the deeper areas.
Due to the high infiltration rate of water on the sandy coastal plain over which such rivers move, it is believed that only 5% of the total annual precipitation is borne by rivers/streams in the Kosi area. The most sensitive area is apparently Lake Nhlange, which can be isolated with the slightest change in drainage patterns. There is a fairly strong seasonal inflow of fresh water into the head of the estuary.
SAND
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. The composition of sand is highly variable, depending on the local rock sources and conditions. Coastal sand is essentially pulverized, weathered rock along with some fragments of shelled creatures and other biota, tossed up by the waves and as sediment from inland areas. Sand is basically the material from broken down rocks, when the rocks weather and decompose over hundreds of thousands and millions of years. Some of the minerals are very unstable and decompose, while others such as feldspar, quartz and hornblende are more stable. Probably the most common composition would be quartz sand with some feldspar. The iron staining on the quartz and iron oxide on the feldspar gives the sand that tan or brownish colour, but this varies greatly.
Some compositions of beach sand around the world:
- Sand that is very white is due to its high quartz content over feldspar and hornblende.
- Then too, sand also trends fairly white, but for a completely different reason: A significant amount of the sand particles are made of calcium carbonate, or the tiny bits of fragmented shells from sea life.
- Some coastal sands contain mainly quartz, and some feldspar. Also small amounts of titanium minerals, namely black ilmenite (titanium and iron oxide) and red brown rutile (titanium oxide) occur in the sand particles.
- Tropical regions have more of this shell-derived sand than temperate regions, where the sand is mostly silica-based in the form of quartz.
- Many beaches have not only white sand but have pink or reddish sand particles as well the origin of this famous coloration is the remains of tiny, single-celled creatures called Foraminifera that have pink or reddish shells.
- Some beaches are well-known for black sand beaches, the result of ground-up, dark volcanic rocks.
- Other sand has a greenish tint due to the presence of the mineral olivine.
WETLAND TYPES
The Kosi Bay System comprises 16 different wetland types, including 1) Shallow marine waters 2) Coral reefs 3) Sand/shingle shores 4) Estuarine waters 5) Tidal mudflats, including intertidal flats and saltflats 6) Salt marshes 7) Mangrove/tidal forest 8) Coastal brackish/saline lagoons 9) Coastal fresh lagoons 10) Deltas 11) Freshwater lakes: permanent 12) Freshwater lakes: seasonal/intermittent 13) Saline/brackish lakes/marches: permanent 14) Saline/brackish lakes/marches: seasonal/intermittent 15) Freshwater marches/pools: permanent 16) Freshwater marches/pools: seasonal/intermittent.
FAUNA AND FLORA
Bird species in the area include the Palm-nut Vulture, Pel's Fishing Owl, White-backed Night-heron, and kingfishers. Duiker, hippopotamus, crocodiles and Bull sharks are also present, and loggerhead and leatherback sea turtles lay their eggs on the beach. The Bay is noted for its aggressive Bull shark population. The sharks are locally known as Zambesi. The Kosi Palm has the largest leaf of any plant. Endemic species include the Kosi cycad and Kosi fern. It is one of very few places on Earth where 5 different species of Mangrove trees are found in one area. Kosi Bay is particularly famous for the traditional Tsonga fish traps built to trap fish moving in and out of the estuary with the tide. The Tsonga people, who have colonised this land for more than 800 years, are experts in fish traps and the construction of fishkraal.
VEGETATION
The vegetation around the lakes and estuary comprises swamp forests (dominant are ferns), marches, sedge and aquatic communities, mangal communities (such as mangroves), coastal dune forests, grassland, open woodland and palm communities.
DISTURBANCES AND THREATS INCLUDING CHANGES IN LAND USE AND MAJOR DEVELOPMENT PROJECTS
Disturbances and threats include slash-and-burn, afforestation, chemicals, population pressure, schemes to develop a harbour in Kosi Bay (appears to have been shelved), mining of Titanium and other heavy metals (though no known plans), the in-filling by sediment of the lakes due to swamp forest destruction, the encroachment of Phragmites reeds around the lakes and channels, noxious weeds (the principal one being Pereskia aculeate, which grows and fruits well in the area), DDT pollution, fish traps used have been perceived as contributing to the sanding-up of the tidal basin.
References:
Ewisa Kosi Bay
58187178,d.ZGU
Ramsar
TINLEY, K. L. – 1985 – Coastal Dunes of South Africa. A report of the Committee of Nature Conservation Research, National Programme of Ecosystem Research - South African National Scientific Programmes Report No 109.
RAMSAY, P. J. – 1997 – Holocene Sea Level Changes in Maputaland focus on the Quaternary evolution of Southeast African Coastal Plain. In: Botha, G. A. (ed), International Union for Quaternary Research Workshop Abstracts, Council for Geosciences, Pretoria, South Africa, pp. 57.
DINGLE, R. V. and ROGERS, J. – 1972 – Pleistocene Paleogeography of the Agulhas Bank - Trans. Roy. Soc. S. Africa 40 (3): 155 – 165.